ESR1 and breast carcinoma: Heterogeneity in ALA-stimulated PpIX fluorescence was found in a panel of human breast cancer cells including ER positive (T47D, MDA-MB-361), HER2 positive (SkBr3, MDA-MB-453) and triple negative (Hs578T, MDA-MB-231) breast cancer cells (Fig. 1a).